An ancient solar observatory

Archaeologists from Yale and the University of Leicester have identified the …

Archaeologists from Yale and the University of Leicester have identified the purpose of a grouping of thirteen towers outside the Incan citadel near Chankillo, Peru. It turns out to be the oldest known solar observatory in the new world. The thirteen towers look like a set of teeth jutting up from the landscape, yet when viewed from a precise location within a temple at Chankillo, the sun will be in an alignment with each of the towers during events that cover the entire solar year. This work was published in last week's edition of Science.

Through recorded accounts from as late as the 16th century, archaeologists had known about the use of a series of towers being used to mark the rising and setting of the sun at various points during the year. Yet until recently, no one knew the location of the towers mentioned. While the citadel at Chankillo had been known and studied for some time, there had been considerable debate about the role of the mounds located on a hill about 300 meters from the main structure. Ivan Ghezzi, the graduate student who made the discovery had originally been studying ancient warfare, focusing at that time on the citadel. However, as far back as the 19th century there had been speculation that the array of towers could have had a use in some form of astronomical prediction, however, no one had investigated this very far beyond speculation. As Ghezzi himself put it, "We were there. We had extraordinary support from the Peruvian Government, Earthwatch and Yale University. So we said, 'Let's study it while we are here!'"

Shortly after beginning to take measurements to explore the hypothesis that the 13 towers had to do with astronomy, the researchers found that one tower aligned with the June solstice and another with the December solstice! While doing this proved to be a straight forward task; accurately dating the structures was much more arduous. What they found was that the towers were much older than they thought. Dating suggested that the towers were constructed around the 4th century B.C., making them over 2,300 years old. According to Ghezzi, "Chankillo reflects well-developed astronomical principles, which suggests the original forms of astronomy must be quite older," than previously believed. This is by far the oldest discovery of its kind in the Americas and shines light on just how advanced previous cultures were.

Matt Ford / Matt is a contributing writer at Ars Technica, focusing on physics, astronomy, chemistry, mathematics, and engineering. When he's not writing, he works on realtime models of large-scale engineering systems.